Gas chromatographic properties of some liquid crystals containing dioxyethylene ether terminal chains

Comparative gas chromatographic properties of four rod-like liquid crystals coated on capillary columns are studied. These four liquid crystals contain the same number of atoms in their backbones. They differ by the partial or total replacement of the two terminal heptyloxy chains by a 2-(2-methoxyethoxy)ethoxy (called also dioxyethylene ether) chain. Synthesis and thermal properties of these four liquid crystals are presented. It appears that the introduction of dioxyethylene ether decreases the two transition temperatures as well as the nematic range. With regards to the chromatographic separation abilities, the four liquid crystals are efficient before and after solid-nematic or nematic-liquid transitions; however, the plate numbers are higher in the nematic state. Interesting analytical applications are demonstrated in different fields : isomeric separation of alkanes, aromatics, polyaromatics, volatile aroma compounds, cis and trans isomers and phenols. The increase of the number of oxyethylene units permits to drastically increase the separation efficiency for polar solutes.